Substrates made from a ceramic material are known per se. They are generally composed of a thin sheet of sintered ceramic material, such as the binary compounds aluminum oxide (Al.sub.2 O.sub.3), magnesium oxide (MgO), beryllium oxide (BeO), aluminium nitride (AlN) or silicon carbide (SiC). Substrates made from ternary compounds, such as MgSiN.sub.2, are also known. Because of their satisfactory electrically insulating properties, the known substrates are used in passive and active electrical components, such as resistors, capacitors, transformers and power transistors. In these applications, they serve as supports of current-conducting structures. In U.S. Pat. No. 5,411,924, filed by Applicant, the advantages and disadvantages of a number of substrates are briefly stated.
An important field of application of ceramic substrates is formed by the Si-semiconductor technology. Substrates suitable for said technology must have a high electrical resistance R (ohm), a satisfactory strength .sigma. (MPa) and a high thermal conductance, k (W/m.K). In addition, the coefficient of expansion .alpha. (l/K) of the substrates should be substantially equal to that of Si. The last-mentioned measure ensures that Si structures provided on the substrate do not crack and/or become detached under the influence of variations in temperature. The coefficient of expansion of silicon is approximately 4.8.10.sup.-6 K.sup.-1.
As a result of these requirements, the use of magnesium oxide and aluminium oxide as the substrate material is not optimal because their thermal conductance is too low and their coefficient of expansion is too high. These disadvantages apply in particular when these substrates are used in large Si-semiconductor structures and/or "power devices". The coefficient of expansion of MgSiN.sub.2 (5.8.times.10.sup.-6) is much closer to that of Si than that of aluminum oxide and magnesium oxide. However, particularly in the case of relatively large substrate surfaces of MgSiN.sub.2, on which complex semiconductor structures are provided, the difference between the coefficients of expansion of Si and MgSiN.sub.2 is still too large. Ceramic substrates of silicon carbide are relatively expensive because this material is difficult to process. In addition, silicon carbide has a relatively high dielectric constant. As a result, this material is less suitable for use as a substrate in electronic components. Ceramic bodies of beryllium oxide have the important disadvantage that they comprise toxic beryllium. Substrates of aluminium nitride exhibit a favourable, high thermal conductance (approximately 150 W/m.K) and a coefficient of expansion (4.8.10.sup.-6 K.sup.-1) which is substantially identical to that of Si. However, this material is difficult to manufacture and hence relatively expensive.